The present invention relates to high-speed production units for machining operations, of the type comprising means for supporting the piece being machined in a fixed position and a horizontal-axis spindle which carries a machining tool and is mounted, in such a way that it is turns, in a spindle-headstock structure that is displaceable along a horizontal axis Z parallel to the axis of the spindle, along a horizontal axis X perpendicular to the axis of the spindle, and along a vertical axis Y, said production unit comprising:
a fixed supporting structure;
a first slide mounted so that it slides on said fixed structure along one first of the aforesaid three axes X, Y, Z;
a second slide mounted so that it slides on said first slide along one second of the aforesaid three axes X, Y, Z; and
a third slide mounted so that it slides on said second slide along the third of the aforesaid three axes X, Y, Z, and is connected to the aforesaid spindle-headstock structure or quill.
A production unit of the type specified above is, for example, described and illustrated in the European patent EP 0 648 574. Another known machine of the type specified above is illustrated in the European patent application EP 0 742 072.
These known machines have characteristics such as to enable displacements of the spindle at high speeds, with consequent high accelerations, so as to achieve an accordingly high production capacity. Of course, the trend of recent years to design machines that are increasingly faster and are subjected to high accelerations consequently imposes the need to guarantee that the moving parts of the machine are not subjected to inclinations or deformations as a result of the accelerations and decelerations which the machine undergoes. The corresponding loads and stresses are of course all the higher, the higher the mass of the moving bodies.
The purpose of the present invention is to provide a production unit of the type specified above, which, on the one hand, is able to operate at high speeds and with high accelerations, and, on the other, can guarantee the necessary characteristics of stiffness and stability, albeit with a relatively simple and light structure.
With a view to achieving the above purpose, the subject of the invention is a production unit having the characteristics specified at the beginning of the present description, the said production unit being moreover characterized in that:
the fixed supporting structure comprises a machine bed and a fixed portal frame comprising two side uprights and a top structure that connects the uprights together;
the aforesaid first slide is a cross member mounted so that it slides along said vertical axis Y between the two uprights of the fixed portal frame;
the aforesaid second slide is a carriage mounted so that it slides underneath the aforesaid cross member along the said horizontal axis X; and
the aforesaid third slide, which is rigidly connected to the spindle-headstock structure or quill, is mounted so that it slides underneath said second slide or carriage along the aforesaid horizontal axis Z parallel to the axis of the spindle.
The particular succession (Y-X-Z) with which the axes of the production unit are cascaded, starting from the fixed structure down to spindle-headstock structure cannot be found in any known structure and enables a series of considerable advantages to be achieved, as will emerge from the ensuing description.
In a first embodiment, the said vertically mobile cross member is provided with a central column or fin rigidly connected to the cross member and extending upwards starting from the latter, said central column being guided in a sliding way through said top structure of the fixed portal frame. In addition, preferably at least one linear electric motor is provided for controlling the mobile cross member, said motor including a stator assembly mounted on said top structure of the fixed portal frame, and a mobile assembly mounted on said central column. In order to control vertical displacement of the cross member, the latter is subjected to a force applied at the aforesaid central column, at the centre of the cross member and at the centre of the fixed portal frame. This makes it possible to reduce considerably the vibrations to which the cross member may be subjected as a result of its own accelerations and decelerations.
In a second embodiment, the aforesaid vertical column or fin is absent, and the cross member has two front lateral guides and two rear lateral guides set symmetrically with respect to a vertical plane passing through the centroid of the cross member. In this case, the cross member is preferably controlled by two pairs of linear electric motors, each of which has a stator connected to an upright of the fixed portal frame, and a mobile assembly connected to one side of the cross member, the arrangement being such that the resultants of the forces applied by the two pairs of motors on the cross member are contained in a plane orthogonal to the axis Z passing through the centroid of the cross member.
Thanks to the above characteristics, in both embodiments described above it is possible to operate with considerably high accelerations and decelerations, and hence with a very high productivity, at the same time guaranteeing perfect stability of the mobile parts and the absence of flexural oscillations or torsional vibrations of the said parts, notwithstanding the fact that they have a relatively simple and light structure.
A further advantage of the particular structure and arrangement described above lies in the fact that the area of the machine bed on which the piece to be machined is set is free from guides for sliding of moving parts of the machine. Consequently, there is a complete elimination of the problem that arises in certain known machines, in which the swarf may fall on said guides, thus creating problems as regards movement of the mobile part which slides on said guides.
According to a further preferred characteristic of the invention, the aforesaid vertically mobile cross member is supported laterally by two hydraulic cylinders which substantially balance its weight, typically two hydraulic cylinders, each of which is supplied by an accumulator of hydraulic fluid under pressure.
Again owing to the particular arrangement described above, the machine according to the invention presents very reduced overall dimensions at the front (in a plane perpendicular to the axis of the spindle). Thanks to the complete separation between the area where the slide guides for the moving parts of the machine are present and the area supporting the workpiece, also draining and emptying-off of the coolant and the swarf can be carried out in a simpler and more efficient way.
The use of linear motors, the application of which to machines of this type is on the other hand already known, is optimal on account of the characteristics of speed and precision of this type of motors. For this reason, also the slide which moves along the X axis and the slide which moves along the Z axis are preferably controlled by linear electric motors. However, it is also possible to envisage a drive with rotating electric motors and ball-screw transmission systems for any axis of the machine.
Further characteristics that form the subject of the present invention are specified in the claims. The advantages of the invention will emerge from the ensuing description, with reference to the attached drawings, which are provided purely to furnish non-limiting examples, and in which: